Phenol-formaldehyde binder is the glue that holds glass fibers together in wool insulation. Phenolic binders have been holding glass wool together since the late 1930's.
In a fiber-forming operation the usual practice is to spray apply an uncured binder, such as a phenol-formaldehyde condensate in solution form, to newly attenuated fibers so that the fibers are wetted with the uncured binder. Fibers of this character are collected in a mass upon a moving conveyor. The thickness of the mass is controlled to provide a fibrous batt which is conveyed or passed through an oven or curing zone for curing the binder in the batt.
Curing usually is accomplished in an oven heated to a temperature of 400.degree. F. The curing operation compresses the glass fibers and binder to a desired thickness and heats them for 30 seconds. Because the operation forces hot air through a product designed to be a thermal insulator, the amount of heat in the insulation varies and therefore the degree of cure of the thermoset resin is variable.